Upon a vehicle cold start, the exhaust catalyst is heated, as well as engine and transmission lubricants. Catalyst heating may be achieved via the exhaust gas by retarding engine spark timing relative to peak torque timing or MBT (minimum spark advance for best torque). Further, as a result of engine operation, waste engine heat warms the powertrain lubricants, reducing lubricant viscosity (and decreasing engine friction) and thus improving fuel economy. Spark timing retard increases exhaust temperature, but does nothing to increase lubricant temperature. Nevertheless, due to emission requirements and catalytic converter performance, exhaust heat is generally prioritized higher relative to lubricant heating.
One approach to provide additional and more rapid heating to engine and transmission lubricants during engine start-up is presented in U.S. 2007/0137594. Specifically, a heat-exchange liquid circuit connected to a heat storage device controls engine lubricant temperature. Oil temperature is detected by a temperature sensor such that when oil temperature is lower than the desired temperature and lower than the heat exchange fluid, heat can be transferred to the oil to increase oil temperature and thus reduce viscosity.
However, the heat storage device may have limited heat capacity. As such, after long vehicle-off durations, there may be little to no additional heat available for transfer to the lubricant.
In one example, the above issues may be addressed by a method for controlling the warming of powertrain lubricants during engine warm-up from a cold start, the engine having an output crankshaft, comprising: selectively driving a lubricant heating device with the crankshaft during the cold start based on lubricating oil temperature; and directing the powertrain lubricants to the lubricant heating device. In some examples, the lubricant heating device is a shear device that is selectively coupled to the engine crankshaft, such that the device and the crankshaft are mechanically coupled at lower temperatures, and mechanically de-coupled at higher temperatures.
By selectively converting engine crankshaft torque into heat for lubricating oil based on the oil temperature, it is possible to decrease powertrain friction and improve fuel economy earlier during engine warm-up under appropriate conditions, without necessarily reducing exhaust heating. Rather, by increasing shaft torque during the cold start, exhaust heating can be maintained while increasing lubricant heating. Specifically, the fuel cost of increasing engine shaft work is countered by applying the shaft work to heat lubricants and thereby reduce friction. And, in some examples, sufficiently high exhaust temperatures may be achieved via the increased engine output such that less spark retard may be possible while still sufficiently heating the exhaust catalyst, thereby further reducing fuel consumption due to reduced spark-related losses. While the controlled heating torque is available, the need for fast acting torque reserve (via spark retard) may also be reduced, thus further reducing fuel consumption.
The heated lubricant may include one or both of engine and transmission oil. However, various other powertrain lubricants may also be used.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.